1. Field of the Invention
The present invention relates to a system for adjusting the optical axis of a semiconductor laser apparatus, and more specifically, to a system for adjusting the optical axis of a semiconductor laser apparatus by aligning a semiconductor laser and an optical system.
2. Description of the Prior Art
The following is a conventional method for adjusting the optical axis of a semiconductor laser apparatus. First, as shown in FIG. 1, a lens 4 is incorporated into a barrel 3. One surface of the barrel 3 is used as a reference surface PS, which is a plane surface serving as a reference for indicating a position at which a point image of a laser beam LE emitted from a light emitting point LP is formed. The laser beam LE is converged at a position a predetermined distance away from the reference surface PS.
A concave C is formed in a fixing member 1. The concave C is in a predetermined positional relationship with a photosensor 2 fixed to the fixing member 1. The photosensor 2 comprises a light receiving device such as a pin photodiode or a charge coupled device (CCD). A light receiving surface 2a of the photosensor 2 corresponds to a light receiving surface of an apparatus for which the semiconductor laser apparatus of FIG. 1 is actually employed. For example, when the semiconductor laser apparatus is employed in a printer for forming a latent image on a photoreceptor, the surface of the photoreceptor is the light receiving surface. By fitting the barrel 3 in the concave C in such manner that the reference surface PS abuts the inner surface of the concave C as shown in FIG. 1, the reference surface PS and the light receiving surface 2a become parallel to each other, and the position at which the point image is formed coincides with a predetermined position FP on the light receiving surface 2a.
Then, a semiconductor laser 6 is incorporated into a laser holder 5. The laser holder 5 is pushed in the direction of arrow ml by means of a collet 7 so as to abut the barrel 3 fitted in the fixing member 1. In doing so, a plane FB of the laser holder 5 is brought into contact with a plane FA of the barrel 3. The plane FA is parallel to the reference surface PS.
Then, an alignment in the X and Y directions is performed while signals from the photosensor 2 are being referred to. The alignment is performed by shifting the laser holder 5 in the X and Y directions by means of the collet 7 while the plane FA is in contact with the plane FB. As shown in FIG. 9, the X direction and the Y direction correspond to the minor axis direction and the major axis direction of a far field pattern, respectively, and the Z direction corresponds to a direction vertical to the X-Y plane. The alignment in the Z direction is performed by means of a non-illustrated mechanism.
The laser holder 5 is fixed to the barrel 3 at an optimum position, i.e. at a position which causes an optical axis X1 of the lens 4 and an optical axis X2 of the semiconductor laser 6 to coincide with each other as shown in FIG. 1. This fixing is performed by a spot welding by means of a YAG laser LW. The fixing may be performed by means of an ultraviolet setting adhesive.
However, in this system for adjusting the optical axis of a semiconductor laser apparatus, if the optical axis X1 of the lens 4 or the optical axis X2 of the semiconductor laser 6 is not vertical to the reference surface PS, an optimum point image characteristic cannot be attained only by the alignment in the X and Y directions. That is, the intensity distribution of the point image formed on the photosensor 2 becomes non-uniform. The inclination of the optical axis X1 occurs when the lens 4 incorporated in the barrel 3 is misoriented. The inclination of the optical axis X2 occurs when a laser chip (not shown) die-bonded in the semiconductor laser 6 is inclined or when the semiconductor laser 6 is incorporated in the laser holder 5 improperly.